While Hollande’s commitment to proposed legislation allowing same-sex marriages has been questioned in recent weeks, Trierweiler revealed she had accepted an invitation to participate in the wedding of gay friends.
She said she was delighted to have a role at one of the very first such marriages in France.
A law providing for same sex couples to wed and adopt children is expected to be on the French statute book by the middle of next year.
Its passage through parliament is likely to be stormy though, given strong opposition from sections of the opposition right, Catholic bishops and other religious leaders.
Hollande attempted to calm the debate last month by announcing that mayors would not be obliged to officiate at gay weddings if they did not agree with them on principle.
That prompted allegations of "treachery" from France's main gay lobby, which accused the president of legitimising homophobia.
Tens of thousands of protestors took to the streets of Paris last month in opposition to the government's plans but opinion polls suggest most voters support the planned reform.
Representatives of the main parties in parliament agreed on Tuesday that the main debate on the draft legislation will take place in the first week of February.